The following information is provided to assist the reader in understanding technologies disclosed below and the environment in which such technologies may typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless clearly stated otherwise in this document. References set forth herein may facilitate understanding of the technologies or the background thereof. The disclosure of all references cited herein are incorporated by reference.
Acute and chronic diseases of the lung remain major healthcare problems. The American Lung Association reports that nearly 350,000 Americans die each year of some form of lung disease. Lung disease is the number three killer of Americans and is responsible for one in seven deaths. Acute lung failure and adult respiratory distress syndrome (ARDS) are prevalent forms of lung disease. ARDS afflicts about 150,000 Americans each year. The associated mortality of ARDS remains between 40 and 60% despite improvements in critical care medicine. Most lung disease, however, is chronic. Emphysema and chronic bronchitis, two forms of chronic obstructive pulmonary disease (COPD), afflict over 14 million Americans annually. Chronic lung disease is now the 3rd leading cause of death in America, claiming the lives of over 400,000 annually and carrying a cost of $154 billion. As chronic lung disease reaches end stage, lung transplantation becomes the only choice for effective treatment. Lung transplantation has had a steady rise over the last 10 years and ˜3300 lung transplants are performed annually worldwide. The average time on the waiting list varies from 6 to 12 months depending on the patient's condition and institutional expertise, and 10-15% of patients die while on the waiting list in the US. A narrow window of opportunity exists for lung transplant in any patient who is sick enough to benefit from the operation, but healthy enough to survive months of waiting for a donor lung and then the subsequent surgery.
Once they reach a critical condition, mechanical ventilation and extracorporeal membrane oxygenation (ECMO) are the only alternatives for respiratory support available to bridge acute and chronic respiratory patients to lung recovery or lung transplantation. Mechanical ventilation (MV) may maintain adequate gas exchange for short term support, but in longer term support can lead to ventilator induced lung injury from barotrauma (high pressure), volutrauma (over-distension), and biotrauma (molecular and cell mediated inflammation), which can further worsen the respiratory status of the patient. ECMO is expensive and complicated, requiring the use of an external pump and blood circuit that have to be supervised continuously by highly trained technicians. The confinement of the patient in MV and especially ECMO leads to a progressive deconditioning that is reflected in higher postoperative complications and earlier mortality after transplant. Nevertheless, ECMO has been increasingly considered as the only alternative to bridge patients to lung transplant or lung recovery after an acute decompensation from their disease. More recently, with increasing experience at active transplant centers and improvement in ECMO technology, the concept of “ambulatory ECMO” has gained popularity and facilitates and expedites patient recovery after transplantation. Success in ambulatory ECMO underscores the importance of maintaining patient mobility. Currently available ambulatory ECMO systems combine existing blood pumps and bypass oxygenators into an integrated system, but remain bulky and cumbersome and require frequent exchange of the oxygenators for longer term support.
Recent success with paracorporeal left ventricular assist devices (VADs) for heart failure patients has stimulated envisioning an ambulatory pump-lung device that can be a bridge to lung transplant or recovery. No fully integrated ambulatory pump-lungs are being used clinically, however. Portable or ambulatory systems under development integrate a separate blood pump and oxygenator under a single controller unit, but remain cumbersome. In such devices, a blood pump is typically connected by one or more conduits (for example, lengths of tubing) to an oxygenator. While a number of systems have integrated blood pumps, the blood leaving the impeller unit of these devices typically travels through channels before being distributed by manifolds into the hollow fiber bundle compartment.